Liquid rocket engine injector with variable flow area

ABSTRACT

A variable flow area injector for a liquid rocket engine. The injector has a poppet with a variable outer width portion and a housing with a variable inner width portion. An annular flow path is defined between the variable width portions. Increased throttling of the engine passively increases the annular flow area of the injector by forcing the poppet in a distal direction. Decreased throttling allows a restoring spring to move the poppet in a proximal direction to decrease the annular flow area. A bellows can be included to dampen movement of the poppet. The bellows may be in a propellant-filled cavity separate from the main propellant flow path and have a series of openings through which the separate propellant flows.

CROSS-REFERENCE TO RELATED APPLICATION

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57. Forexample, the present application is a continuation of U.S. patentapplication Ser. No. 17/453,580, filed on Nov. 4, 2021, and titled“LIQUID ROCKET ENGINE INJECTOR WITH VARIABLE FLOW AREA,” the entirecontent of which is incorporated by reference herein and forms a part ofthis specification for all purposes.

BACKGROUND Field

This development relates to rocket engines, in particular to liquidrocket engine injectors.

Description of the Related Art

Liquid rocket engines allow for throttled thrust. However,deep-throttling of the engine can create challenges for propellantinjectors. One challenge of deep throttling a rocket engine isminimizing the pressure drop across the injector, while avoidingcoupling between the feed system and the thrust chamber. There is a needfor improved injectors that address these and other challenges withliquid rocket injectors.

SUMMARY

The embodiments disclosed herein each have several aspects no single oneof which is solely responsible for the disclosure's desirableattributes. Without limiting the scope of this disclosure, its moreprominent features will now be briefly discussed. After considering thisdiscussion, and particularly after reading the section entitled“Detailed Description” one will understand how the features of theembodiments described herein provide advantages over existing approachesto injectors for rocket engines.

A rocket combustion chamber injector having a passively varying flowarea is described. The injector comprises a housing, a poppet, a springand a bellows. The housing comprises a sidewall extending along alongitudinal axis between a proximal end and a distal end, where thesidewall is comprising a variable inner width portion and a plurality ofports arranged radially about the longitudinal axis near the variableinner width portion, and the plurality of ports are configured toreceive a propellant along a propellant flow path that extends from theplurality of ports towards the distal end of the housing. The poppetextends axially between a proximal end and a distal end, the poppet ismoveable within the housing along the longitudinal axis, the distal endof the poppet has a variable outer width portion located radiallyinwardly of the variable inner width portion of the housing to definetherebetween an annular flow area of the propellant flow path, and thevariable outer width portion is configured such that propellant flowingalong the propellant flow path around the variable outer width portionapplies a first axial force on the distal end of the poppet. The springis coupled to the proximal end of the poppet within the housing and isconfigured to apply a second axial force on the proximal end of thepoppet. The bellows is located within a cavity at the proximal end ofthe housing, the cavity is configured to receive propellant therein, thebellows is coupled to the proximal end of the poppet and located outsideof the propellant flow path, and the bellows comprises a plurality ofopenings through which propellant is configured to be transmitted todampen movement of the poppet along the longitudinal axis. The poppet isconfigured to move toward the distal end of the housing in response tothe first axial force exceeding the second axial force and therebyincrease the annular flow area, and the poppet is configured to movetoward the proximal end of the housing in response to the second axialforce exceeding the first axial force and thereby decrease the annularflow area.

There may be a variety of embodiments of the above and other aspects.The injector may further comprise an orifice holder supporting anorifice that is in fluid communication with the cavity at the proximalend of the housing. The injector may further comprise a first hard stopand a second hard stop configured to limit axial travel of the poppetwithin the housing to thereby limit a maximum area and a minimum area ofthe annular flow area. The injector may further comprise a guide withinthe housing configured to radially support the poppet during axialmovement of the poppet through the guide. A ratio of A) a pressure dropacross the injector to B) a pressure within a combustion chamber influid communication with the injector, may be maintained within a targetrange across a range of flow rates. The ratio may be controlled within atarget range of 15% to 25% across the range of flow rates.

In another aspect, a rocket combustion chamber injector having apassively varying flow area is described. The injector comprises anelongated housing, an elongated poppet, a spring and a bellows. Theelongated housing extends from a proximal end to a distal end to definea longitudinal axis, and the housing comprises a variable inner widthportion and a plurality of ports arranged proximally of and adjacent tothe variable inner width portion and partially defining a propellantflow path that exits out the distal end of the housing. The elongatedpoppet is supported within the housing and moveable axially, and thepoppet comprises a variable outer width portion located radiallyinwardly of the variable inner width portion of the housing to definetherebetween an annular flow area of the propellant flow path. Thespring is located within the housing and is configured to bias thepoppet in a proximal direction. The bellows is located within a cavityat the proximal end of the housing and located outside of the propellantflow path, and the cavity is configured to be filled with propellant.The poppet is configured to move in a distal direction in response to anincreased propellant flow along the propellant flow path to therebyincrease the annular flow area and to move in the proximal direction inresponse to a decreased propellant flow along the propellant flow pathto thereby decrease the annular flow area.

There may be a variety of embodiments of the above and other aspects.The variable inner width portion may increase in inner width in thedistal direction. The plurality of ports may be arranged radially aboutthe longitudinal axis. The propellant flow path may bend from theplurality of ports toward the distal end of the housing. The variableouter width portion of the poppet may increase in outer width in thedistal direction. The variable outer width portion of the poppet may beconfigured such that propellant flowing along the propellant flow patharound the variable outer width portion applies a first axial force inthe distal direction on the variable outer width portion of the poppet.The spring may be configured to apply a second axial force in theproximal direction on the poppet. The increased propellant flow alongthe propellant flow path may cause the first axial force to exceed thesecond axial force to thereby move the poppet in the distal direction.The decreased propellant flow along the propellant flow path may causethe second axial force to exceed the first axial force to thereby movethe poppet in the proximal direction. The bellows may comprise aplurality of openings through which propellant is configured to betransmitted to dampen movement of the poppet along the longitudinalaxis. The bellows may be located proximally of the poppet and provide adamping force to a proximal end of the poppet. A ratio of A) a pressuredrop across the injector to B) a pressure within a combustion chamber influid communication with the injector, may be maintained within a targetrange across a range of flow rates. The ratio may be controlled within atarget range of 15% to 25% across the range of flow rates.

In another aspect, a rocket combustion chamber is described. The rocketcombustion chamber comprises an injector plate and a plurality ofvariable flow area injectors. The plurality of variable flow areainjectors are configured to inject propellant through the injectorplate. Each variable flow area injector comprises an elongated housing,an elongated poppet, a spring, and a bellows. The elongated housingextends from a proximal end to a distal end to define a longitudinalaxis, and the housing comprises a variable inner width portion and aplurality of ports arranged proximally of and adjacent to the variableinner width portion and partially defining a propellant flow path thatexits out the distal end of the housing. The elongated poppet issupported within the housing and is moveable axially, and the poppetcomprises a variable outer width portion located radially inwardly ofthe variable inner width portion of the housing to define therebetweenan annular flow area of the propellant flow path. The spring is locatedwithin the housing and is configured to bias the poppet in a proximaldirection. The bellows is located within a cavity at the proximal end ofthe housing and is located outside of the propellant flow path, and thecavity is configured to be filled with propellant. The poppet isconfigured to move in a distal direction in response to an increasedpropellant flow along the propellant flow path to thereby increase theannular flow area and to move in the proximal direction in response to adecreased propellant flow along the propellant flow path to therebydecrease the annular flow area.

In another aspect, a method of injecting propellant into a rocketcombustion chamber is described. The method comprises increasing apropellant flow through a plurality of ports of a housing of an injectoralong a propellant flow path that at least partially extends in a distaldirection, impinging the propellant flow on a variable outer widthportion of an axially moveable poppet, moving the poppet distally suchthat the variable outer width portion of the poppet moves distallywithin a variable inner width portion of the housing to increase anannular flow area therethrough, decreasing the propellant flow throughthe plurality of ports, biasing the poppet in a proximal direction usinga compression spring, dampening movement of the poppet with a bellows ina propellant-filled cavity that is separate from the propellant flowpath, and moving the poppet proximally such that the variable outerwidth portion of the poppet moves proximally within the variable innerwidth portion of the housing to decrease the annular flow areatherethrough. In some embodiments, the further comprises flowing thepropellant radially through the plurality of ports and axially out of adistal end of the injector.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will becomemore fully apparent from the following description and appended claims,taken in conjunction with the accompanying drawings. Understanding thatthese drawings depict only several embodiments in accordance with thedisclosure and are not to be considered limiting of its scope, thedisclosure will be described with additional specificity and detailthrough use of the accompanying drawings. In the following detaileddescription, reference is made to the accompanying drawings, which forma part hereof. In the drawings, similar symbols typically identifysimilar components, unless context dictates otherwise. The illustrativeembodiments described in the detailed description, drawings, and claimsare not meant to be limiting. Other embodiments may be utilized, andother changes may be made, without departing from the spirit or scope ofthe subject matter presented here. It will be readily understood thatthe aspects of the present disclosure, as generally described herein,and illustrated in the figures, can be arranged, substituted, combined,and designed in a wide variety of different configurations, all of whichare explicitly contemplated and make part of this disclosure.

Described herein are embodiments of injectors for a liquid rocketpropulsion system. The injector passively varies the cross-sectionalarea of fluid flow across the injector as the throttle is increased anddecreased. The area changes based in part on the velocity of the fluidflow—the higher the velocity, the larger the area, and vice versa. Thearea is larger in part because a poppet or bluff body moves more in thehigher velocity flow, thus increasing the flow area. The injector mayinclude hard stops for the poppet that provide minimum and maximum flowareas. In some embodiments, the poppet does not rest on the hard stops,so that flow area is continuously varied.

FIG. 1A is a side view of an embodiment of rocket combustion chamber.

FIG. 1B is an end of view of an embodiment of a rocket injector plate ofthe chamber of FIG. 1A and having a plurality of variable flow areainjectors.

FIG. 2A is a cross-sectional view of the variable flow area injectors ofFIG. 1B.

FIGS. 2B and 2C are cross-section views of the injector as taken alongthe line 2B-2B as indicated in FIG. 2A showing the variable annular flowarea, respectively, with smaller and larger flow areas.

FIGS. 3A-3C are various data plots showing the pressure drop across theinjector versus a range of throttling levels, as well as predictive datafrom an analytical model, for various embodiments of the injector ofFIG. 2A.

DETAILED DESCRIPTION

The following detailed description is directed to certain specificembodiments of the development. Reference in this specification to “oneembodiment,” “an embodiment,” or “in some embodiments” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment of thepresent disclosure. The appearances of the phrases “one embodiment,” “anembodiment,” or “in some embodiments” in various places in thespecification are not necessarily all referring to the same embodiment,nor are separate or alternative embodiments necessarily mutuallyexclusive of other embodiments. Moreover, various features are describedwhich may be exhibited by some embodiments and not by others.

Various embodiments will now be described with reference to theaccompanying figures, wherein like numerals refer to like elementsthroughout. The terminology used in the description presented herein isnot intended to be interpreted in any limited or restrictive manner,simply because it is being utilized in conjunction with a detaileddescription of certain specific embodiments of the development.Furthermore, embodiments of the development may include several novelfeatures, no single one of which is solely responsible for its desirableattributes or which is essential to practicing the present disclosure.

FIG. 1A is a side view of an embodiment of rocket combustion chamber100. The chamber extends from a proximal end 102 to a distal end 104.The chamber 100 includes a barrel portion 106 and a nozzle portion 108located at a distal end of the barrel portion 106. The chamber 100defines a longitudinal chamber axis 110 as shown.

FIG. 1B is an end of view of an embodiment of a rocket injector plate112. The plate 112 may be implemented in the chamber 100 of FIG. 1A. Theplate 112 may be located at or near the distal end 102 of the chamber100 when assembled with the chamber 100. The plate 112 has a top surface114 and an outer edge 116. The top surface 114 may be substantiallyplanar and perpendicular to the chamber axis 110 when assembled. Theedge 116 may be circular.

The plate 112 includes a plurality of variable flow area injectors 200.For clarity, only some of the injectors 200 are labelled in FIG. 1B.Some or all of the injectors 200 may be longitudinally oriented at anangle to the chamber axis 110. In some embodiments, the injectors 200may be oriented axially, radially, angled, other orientations, orcombinations thereof.

The injectors 200 may form a number of small diameter flow pathsarranged in patterns through which the fuel and oxidizer travel. Forexample, the flow paths can be arranged in carefully constructedpatterns that optimize the flow of fuel and oxidizer through the flowpaths. The speed of the flow may be determined by the square root of thepressure drop across the injectors 200, the shape of the flow pathsand/or openings in the injector plate 112, and other factors such as thedensity of the propellant.

The injectors 200 and/or injector plate 112 may include a number ofholes. The holes may range in width or diameter from about 0.125 inches(in.) to about 1 in, from about 0.25 in. to about 0.75 in., from about0.375 in. to about 0.5 in., or other larger or smaller sizes. The holesmay be oriented to aim jets of fuel and oxidizer to collide. The jetsmay collide at a point in space a distance away from the injector plate112. The jets may collide at a distance of no more than 0.5 in, 1 in., 2in., 3 in., 4 in., 5 in., 10 in., 20 in., or other distances, from theplate 112. This helps to break the flow up into small droplets that burnmore easily. The injectors 112 may be arranged to form a variety ofdifferent injector layouts, such as shower head, self-impinging doublet,cross-impinging triplet, centripetal or swirling, pintle, other suitablearrangements, or combinations thereof.

FIG. 2 is a cross-sectional view of an example variable flow areainjector 200 according to the present disclosure. The injector 200 iselongated and extends along a longitudinal axis 210. The injector 200includes a housing 212. The housing 212 provides a structural cover andsupport to the injector 200. The housing 212 extends from a proximal end214 to a distal end 216. The distal end 216 may be positioned at achamber of a rocket engine to expel propellant through an outlet 222 andinto the chamber for combustion therein. The housing 212 includes aproximal portion 218 and a distal portion 220. The proximal and distalportions 218, 220 may be separate parts that attach together, or thehousing 212 may be unibody. “Proximal” and “distal” refer to thedirections as shown in FIG. 2 .

The housing 212 includes a plurality of ports 224 through whichpropellant flows into the injector 200. There may be one, two, three,four, five, six, seven, eight, nine, ten or more ports 224. The ports224 may be openings in a sidewall of the housing 212, such as in thedistal portion 220. The ports 224 may be located annularly on all sidesof the housing 212. The ports 224 as shown define openings through whichpropellant flows radially or substantially radially. “Radial” refers toa direction perpendicular to the axis 210. The housing 212 includes anupstream chamber 226. The chamber 226 may receive the propellant and belocated upstream of a variable flow area 280 described in detail below.The ports 224 may open into the chamber 226.

The housing 212 may include a variable inner width portion 228. Theportion 228 may be located distally of the chamber 226. The portion 228may increase in width, e.g. diameter, along the distal direction. Theportion 228 may include a proximal lip as shown such that thecross-sectional area decreases slightly before increasing in the distaldirection. The cross-sectional area of the housing 212 may thus increasein a section that is distal to the proximal lip. In some embodiments,there may not be a lip, and so the cross-sectional area of the housing212 may increase in the distal direction from the chamber 226. Theportion 228 may have a nozzle-opening type shape with a minimum widththroat portion, which may be located closer to the proximal end of theportion 228 than to the distal end. The portion 228 may be conical orfunnel-shaped. The portion 228 opens into the downstream chamber portion230. The portion 230 may be cylindrical as shown. The portion 230 mayhave a constant cross-sectional area. The portion 230 ends in thecircular outlet 222.

The injector 200 includes a poppet 240. The poppet 240 extends distallyfrom a flange 242 at a proximal end thereof. The flange 242 is at theproximal end of an elongated first portion 246. The first portion 246includes a flange 248 located along the length of the first portion 246.At a distal end of the first portion 246 is a relatively wider secondportion 250. The second portion 250 extends into the chamber 226. Thesecond portion 250 narrows in width to a neck 252.

The poppet 240 includes a variable outer width portion 244. The portion244 may be located at a distal end of the poppet 240 as shown. Theportion 24 may connect to the neck 252. The portion 244 increases inouter width in a distal direction. The portion 244 may have a conical orfunnel shape. The portion 244 may include a constant-width orconstant-diameter cylindrical portion located distally of theincreasing-width portion. The portion 244 may be hollow or have a boretherein, for example to reduce weight and improve moving response timeof the poppet 240.

The injector 200 includes a variable flow area 280. The area 280 may bean annular area. The area 280 may be formed between the variable innerwidth portion 228 of the housing 212 and the variable outer widthportion 244 of the poppet 240. As described in further detail herein,for example with respect to FIGS. 2B and 2C, movement of the poppet 240in an axial direction may vary the size of the area 280 and thus controlthe propellant flow mass rate through, and pressure drop across, theinjector 200.

The injector 200 includes a guide 260. The guide 260 may be anelongated, cylindrical structure with an opening therethrough configuredto receive the poppet 240 and radially guide the poppet 240 as it movesaxially. The guide 260 may be formed of TEFLON™, other suitablematerials, or combinations thereof. The guide 260 may be locatedproximally of the ports 224. Inner surfaces of the guide 260 may slideagainst outer surfaces of and axially direct the wider second portion250 of the poppet 240. The guide 260 may center the poppet 240. In someembodiments, flexural bearings may be used to center the poppet 240,either alternatively or in addition to the guide 260.

The injector 200 may include first and second stops 262, 264. The stops262, 264 are inwardly protruding structures, e.g. discs or othersuitable projections, that limit axial travel of the poppet 240. Thefirst stop 262 limits proximal movement of the poppet 240, and thesecond stop 264 located distally of the first stop 262 limits distalmovement. The stops 262, 264 may limit axial travel of the flange 248 onthe poppet 240. The stops 262, 264 are located within the longitudinalproximal channel 219 of the housing 212. The stops 262, 264 may beadjustable to finely control the range of motion of the poppet 240. Oneor more first shims 266 may be strategically used to control the axialdistance between the stops 262, 264. One or more second shims 268 may beused to control the axial placement of the distal portion 220 within theproximal portion 218 of the housing 212. Additional shims may be used insuitable locations, for example distal of the first stop 262, to locatethe stops 262, 264 in desirable positions. Positioning of the stops 262,264 may affect the performance of the injector 200 as further describedherein. In some embodiments, the injector 200 may not need shims 266and/or 268. For example, the stops 262, 264 may be mechanicallyadjustable within the housing 212. In some embodiments, the injector 200may include contact sensors at the stops 262, 264 to identify when thepoppet 240 contacts the stops 262, 264 and thus when the flow area is ata maximum or minimum, in order to control the throttle.

The injector 200 includes a spring 270. The spring 270 biases the poppet240. The spring 270 biases the poppet 240 in the proximal direction. Thespring 270 may be a compression spring. The spring 270 may be locateddistally of the proximal flange 242 of the poppet 240 within the channel219. The spring 270 may be located proximally of the distal portion 220of the housing 212. The spring 270 may be located proximally of thefirst and/or second stop 262, 264. The spring 270 may apply a force inthe proximal direction against the moveable poppet 240 to restore theposition of the poppet 240, as further described herein. The spring 270may be located separately from the main flow path 278 as shown. Thespring 270 may be located within the injector 200 but not in fluidcommunication with the chamber 226.

The injector 200 includes a bellows 272. The bellows 272 may be aflexible structure configured to compress and elongate. The bellows 272may have a resilient, zig-zag sidewall. The bellows 272 defines anannular structure as shown. The bellows 272 by alternate expansion andcontraction may draw in fluid into a series of openings and expel thefluid out through the openings. The openings may be in the sidewall ofthe bellows 272. The bellows 272 may be located in a proximal channelportion 271 of the channel 219 of the housing 212, which may be in theproximal portion 218 of the housing 212. The bellows 272 may contact aproximal side of the poppet 240. The bellows 272 extend from a distalend to a proximal end. The distal end of the bellows 272 contacts theproximal side of the flange 242. The proximal end of the bellows 272contacts a holder 276. The bellows 272 may partially surround a distalend of the holder 276. The holder 276 and flange 242 axially limitmovement of the bellows 272. The proximal end of the bellows 272 may befixed while the distal end of the bellows 272 may move as the poppet 240moves.

The injector 200 includes an orifice 274. The orifice 274 defines anopening therethrough. Propellant may flow through the opening of theorifice 274 and into the proximal channel portion 271 to be drawn intoand expelled out of the bellows 272 through the series of openings inthe bellows 272. The orifice 274 is located proximally of the bellows272. In some embodiments, the orifice 274 may be located directly in thebellows 272. The propellant flow path within the proximal channelportion 271 may be separate from a main propellant flow path that leadsto the combustion chamber of the rocket engine, as further described.The same fluid flowing across the injector is used in the bellows 272,such as liquid oxygen (LOX) or liquid natural gas (LNG). In someembodiments, the bellows 272 and the spring 270 may be combined. Asshown the bellows 272 is a separate component from the spring 270.

One challenge when incorporating the spring 270 into the injector 200 isthat there may be a coupling between the injector 200 and the combustiondynamics. In order to avoid this, high damping may be employed. Fluidicdamping using the orifice 274 and the series of openings in the bellows272 results in high damping. In some embodiments, a transition time froma maximum to a minimum throttle, or vice versa, is about 0.3 seconds.The damping can be varied by changing the orifice size.

The variable volume in the bellows 272 may create impedance for dampingout the effects of pressure oscillations in the combustion process. Thiscan be tuned by adjusting the flow area into or out of the volume. Twoways to create that flow are to use an inlet orifice and/or openings inthe bellows 272. Forming small holes directly in the baffles can be aneconomical, low cost approach to creating flow into or out of thevolume. Another approach is to use a single precision drilled orifice274. In some embodiments, a single precision drilled orifice 272 may beused. In some embodiments, single or multiple holes drilled directlyinto the bellows 272 may be used. The sizing of direct drilled holes inthe bellows 272 may provide an equivalent effective flow area as asingle orifice.

The injector 200 defines a main propellant flow path 278. The propellantmay be any fuel or oxidizer, such as LOX, hydrogen, LNG, kerosene orhypergols. The path 278 extends through the ports 224, but only one flowpath 278 extending through one port 224 is shown for clarity. The path278 extends through the ports 224, into the upstream chamber 226,through the variable inner width portion 228, and into the downstreamchamber portion 230 through the outlet 222. The portion of the flow path278 extending between the variable inner width portion 228 of thehousing 212 and the variable outer width portion 244 of the poppet 240defines an annular-shaped flow area 280. FIGS. 2B and 2C illustrate howa cross-section of the flow area 280 as taken along the line 2B-2B inFIG. 2A changes as the poppet moves in the distal direction from a firstposition shown in FIG. 2A to a second position.

FIGS. 2B and 2C are cross-section views of the injector 200 showing thevariable annular flow area 280, respectively, with smaller and largerflow areas. The housing 212, such as the distal portion 220 as shown,includes an inner surface 221 defining the variable inner width portion228. The variable outer width portion 244 of the poppet 240 is definedby an outer surface 245 that is opposing the inner surface 221. Theannular flow area 280 is defined between the surfaces 221, 245.

The size of the flow area 280 may be varied by moving the poppet 240axially. Movement of the poppet 240 in the proximal direction will causethe outer surface 245 of the poppet 245 to be closer to the opposinginner surface 221 of the housing 212, thus decreasing the size of theflow area 280 as shown in FIG. 2B. In contrast, as shown in FIG. 2C,movement of the poppet 240 in the distal direction will cause the outersurface 245 of the poppet 245 to be farther from the opposing innersurface 221 of the housing 212, thus increasing the size of the flowarea 280.

The poppet 240 may be moved in the distal direction due to an increasedpropellant mass flow rate along the main flow path 278. The spring 270biases the poppet 240 in the proximal direction. In some embodiments,the bellows 272 may also bias the poppet 240 in the proximal direction.The propellant applies a force on the poppet 240 in the distaldirection. The propellant may apply a drag force on the poppet 240. Thepropellant 240 may also apply normal forces on the poppet 240 with forcevector components in the distal direction that cause it to movedistally. As the mass flow rate of the propellant along the flow path278 increases, an increasing axial force is exerted on the variableouter width portion 244 of the poppet 240 in the distal direction. Whenthe force in the distal direction to the propellant flow is greater thanthe force in the proximal direction due to the spring 270 (and possiblyalso due to the bellows 272), then the poppet 240 will move in thedistal direction. The mass flow rate through the element at a givenpressure drop across the orifice 274 may be increased by increasing thesupply pressure to the element.

The poppet 240 may be moved proximally due to a decreased propellantflow along the main flow path 278. As the propellant mass flow ratedecreases, at some point the proximal forces from the spring 270 (andpossibly the bellows 272) are greater than the distal forces due to thepropellant flow, and thus the poppet 240 will move proximally.

As the poppet 240 moves distally due to increased propellant flow, theflow area 280 increases due to increased separation between the opposingsurfaces of the poppet 240 and the housing 212, as described. This inturn increases the mass flow rate through the injector 200 and therebycontrols (e.g., decreases) the pressure drop across the injector 200, asfurther described herein. Conversely, as the poppet 240 moves proximallydue to decreased propellant flow, the flow area 280 decreases due todecreased separation between the opposing surfaces of the poppet 240 andthe housing 212, as described. This in turn decreases the mass flow ratethrough the injector 200 and thereby controls (e.g., increases) thepressure drop across the injector 200, as further described herein.

Thus, during sufficiently low enough flow velocities, the poppet 240 isforced proximally. The proximal travel of the poppet 240 may be limitedby the upper stop 262. Likewise, the poppet 240 moves distally duringsufficiently high enough fluid drag forces acting on it. The downwardtravel of the poppet 240 is limited by the lower stop 264.

One of the significant challenges in producing a deep-throttling engineis managing the pressure drop across the injector 200. Advantageously,the variable flow area 280 of injectors according to the presentdisclosure may minimize the pressure drop across the injector 200 atmaximum flow rates while avoiding coupling between the fluid injectorsystem and the thrust chamber of the rocket engine. Optimization of thispressure drop while avoiding coupling in this manner is an importantdesign requirement for deep throttling rocket engines. In someembodiments, the injector 200 according to the present disclosure may beused as co-axial injectors in a 1.5 Mlbf engine using LOX/LNG and deepthrottling to 7%. This represents a significant improvement to injectorsfor deep-throttling engines.

Advantageously, the injectors 200 of the present disclosure are highlyconfigurable by adjusting various parameters. In some embodiments, thepreload force due to the spring 272, the spring rate or elasticity ofthe spring 272, the diameter of the orifice 274, the minimum flow area280 and/or the maximum flow area 280 may be configured for optimalperformance in particular engines. The preload force in the compressionspring 272 may be from about 0.5 pound-force (lbf) to about 10 lbf, fromabout 1 lbf to about 5 lbf, from about 1.25 lbf to about 4.5 lbf, fromabout 1.5 lbf to about 4 lbf. The spring rate may be from about 5pound-force per inch (lbf/in) to about 150 lbf/in, from about 7.5 lbf/into about 125 lbf/in, from about 10 lbf/in to about 110 lbf/in, fromabout 25 lbf/in to about 75 lbf/in. The annular flow area 280 may have aminimum flow area from about 0.008 square inches (in²) to about 0.100in², from about 0.010 in² to about 0.050 in², or from about 0.016 squareinches (in²) to about 0.025 in². The annular flow area 280 may have amaximum flow area from about 0.017 square inches (in²) to about 0.250in², from about 0.025 in² to about 0.200 in², from about 0.030 squareinches (in²) to about 0.150 in², or from about 0.035 square inches (in²)to about 0.125 in². It will be understood that these ranges are exampleimplementations and that other preload forces, spring rates, and annularflow areas can be suitably implemented in accordance with the presentdisclosure.

Over the entire throttle range, the pressure drop across the injector(ΔP) needs to be high enough to avoid coupling between the thrustchamber and the feed system. This minimum value is engine dependent andneeds to be determined through testing, but a rule of thumb is that thedimensionless pressure drop, ΔP/P_(C), is above 15%, preferably above20%, where P_(C) is the pressure in the rocket engine combustionchamber. The ΔP/P_(c), versus throttle profile is highly tuneable inembodiments of the present disclosure. Various modes of operation may bedemonstrated by adjusting the spring rate, preload force, and stoppositions. For example, the injector 200 can be adjusted to have thelowest allowable ΔP/P_(c), at high throttle, with providing nearconstant ΔP/P_(c)at lower throttles, decreasing susceptibility tocombustion instabilities without penalizing performance of the enginewith high injector pressure drop at full power. As a further example, inthe event that the combustor does not run stably when the poppet 240 isnot resting on a stop, the injector 200 can be configured to run with akeep-out zone, where the poppet 240 is resting on a stop for most of thethrottle range.

FIG. 3A is a data plot 300 showing the pressure ratio ΔP/P_(c)as apercentage (%) versus throttle percentage (%) for an embodiment of theinjector 200 and having stops 262, 264. The data plot 300 has a firstportion 302 corresponding to the poppet 240, for example the flange 248,bottomed out on the proximal hard stop 262 and thus having a minimumflow area 280. A second portion 304 of the data plot 300 corresponds tothe poppet 240, for example the flange 248, floating between and notcontacting either of the hard stops 262, 264, and thus having a variableflow area 280 that increases as the throttle % increases. A thirdportion 304 of the data plot 300 corresponds to the poppet 240, forexample the flange 248, bottomed out on the distal hard stop 264 andthus having a maximum flow area 280. As shown, the ΔP/P_(c) is greaterthan about 15% over substantially the entire range of throttling, andover the entire range of high throttling. The ΔP/P_(c) may be keptbetween about 15% and about 25% over substantially the entire range ofthrottling. The ΔP/P_(c) may be greater than 15% for throttlepercentages greater than about 20%. The ΔP/P_(c) may be greater than 15%for throttle percentages greater than about 50%, greater than about 60%,greater than about 70%, greater than about 80%, or greater than 90%. Atfull throttle or 100%, the ΔP/P_(c) may be greater than 15% or greaterthan 20%.

FIG. 3B is a data plot 310 showing the pressure ratio ΔP/P_(c) as apercentage (%) versus throttle percentage (%) for an embodiment of theinjector 200 at low throttle and having stops 262, 264. The ΔP/P_(c)increases to about 15% throttle and then decreases after the poppet 240begins to move due to the increased propellant flow. Then, the ΔP/P_(c)decreases to a lower limit at about 30% throttle, due to the hard stopnot allowing the flow area to increase any more. With the flow area 280at a maximum, the ΔP/P_(c) then continually increases as the throttlecontinues to increase.

FIG. 3C is a data plot 320 showing ΔP/P_(c) as a percentage (%) versusthrottle percentage (%) for an embodiment of the injector 200 withcontinuously varying flow area 280. A first set of data 322 is showncorresponding to a manifold pressure of about 600 pounds per square inchabsolute (psia), and a second set of data 324 is shown corresponding toa manifold pressure of about 680 psia. The injector 200 was able to flowwell above 150% throttle level while maintaining a ΔP/P_(c) of just overthe desired 15% level. Due to the large pressure drop across theinjector 200 at these high throttle levels, cavitation began to occur,and at the vertical lines the flow becomes choked due to cavitation. Inaddition, ΔP/P_(c) was increased at lower throttle levels, which wouldyield increased resistance to combustion instability. The ΔP/P_(c)increases to about 20% throttle and then gradually and continuallydecreases after the poppet 240 begins to move due to the increasedpropellant flow. The ΔP/P_(c) decreases continually since there is nohard stop to limit the flow area, and thus the flow area continues toincrease as the throttle % and propellant flow increases. The ΔP/P_(c)continually approaches a horizontal asymptote located between 15% and20%, e.g. at about 17%.

FIG. 3C further shows a third set of data 326 showing predicted resultsfrom an analytical model of the injector 200. In some embodiments, theinjector 200 may be designed to have a desired pressure drop profile.The design may be based on an equation (1) of motion for the poppet 240.The equation (1) may be the following:

$\begin{matrix}{{m\hat{x}} = {{B_{p}\frac{\rho u_{p}^{2}}{2}} - \left( {{kx} + F_{P}} \right) - {{{sign}\left( \overset{.}{x} \right)}\left( \frac{\rho{\overset{\_}{B}}_{b}^{2}B_{b}}{2\left( {A_{b}C_{d,b}} \right)^{2}} \right){\overset{.}{x}}^{2}}}} & (1)\end{matrix}$

In equation (1), m is the mass of the poppet 240, {umlaut over (x)} isthe acceleration of the poppet 240, B_(P) is the base area of the poppet240, p is the density of the injected propellant, u_(p) is the maximumpropellant velocity at the minimum area location of the poppet 240, k isthe restoring force due to the combination of the spring 270 and bellows272, x is the location of the poppet 240 as measured from a no-flowpreloaded position of the poppet 240, F_(P) is the preload force on thepoppet 240, {dot over (x)} is the velocity of the poppet 240, sign({dotover (x)}) is the mathematical positive (+) or negative (−) sign of thevalue of {dot over (x)}, B_(b) is the base area of the bellows 272 and B_(b) is the mean base area of the bellows 272, where the mean base areamultiplied by the height of the bellows 272 gives the volume, to takeinto account the convolutions or corrugations in the wall of the bellows272, A_(b) is the area of the bellows orifice, and C_(d,b) is thedischarge coefficient of the bellows orifice which can be calibratedusing test data.

Using equation (1), the behavior of the injector 200 can be estimated. Amodel based on equation (1) can estimate the forces on the poppet 240and determine its position and the pressure drop across the injector200.

The third set of data 326 in FIG. 3C shows the pre-test prediction usinga calibrated model, which shows close correlation with the test sets ofdata 322, 324. The model based on equation (1) of motion for the poppetcan be used to tune the pressure drop versus throttle to any desiredprofile.

While the above detailed description has shown, described, and pointedout novel features of the present disclosure as applied to variousembodiments, it will be understood that various omissions,substitutions, and changes in the form and details of the device orprocess illustrated may be made by those skilled in the art withoutdeparting from the spirit of the present disclosure. As will berecognized, the present disclosure may be embodied within a form thatdoes not provide all of the features and benefits set forth herein, assome features may be used or practiced separately from others. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

The term “comprising” as used herein is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. Withrespect to the use of substantially any plural and/or singular termsherein, those having skill in the art may translate from the plural tothe singular and/or from the singular to the plural as is appropriate tothe context and/or application. The various singular/plural permutationsmay be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, termsused herein are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to embodiments containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations.

In addition, even if a specific number of an introduced claim recitationis explicitly recited, those skilled in the art will recognize that suchrecitation should typically be interpreted to mean at least the recitednumber (e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations). Furthermore, in those instances where a conventionanalogous to “at least one of A, B, and C, etc.” is used, in generalsuch a construction is intended in the sense one having skill in the artwould understand the convention (e.g., “a system having at least one ofA, B, and C” would include but not be limited to systems that have Aalone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). In those instances where aconvention analogous to “at least one of A, B, or C, etc.” is used, ingeneral such a construction is intended in the sense one having skill inthe art would understand the convention (e.g., “a system having at leastone of A, B, or C” would include but not be limited to systems that haveA alone, B alone, C alone, A and B together, A and C together, B and Ctogether, and/or A, B, and C together, etc.). It will be furtherunderstood by those within the art that virtually any disjunctive wordand/or phrase presenting two or more alternative terms, whether in thedescription, claims, or drawings, should be understood to contemplatethe possibilities of including one of the terms, either of the terms, orboth terms. For example, the phrase “A or B” will be understood toinclude the possibilities of “A” or “B” or “A and B.”

All numbers expressing quantities of ingredients, reaction conditions,and so forth used in the specification and claims are to be understoodas being modified in all instances by the term “about.” Accordingly,unless indicated to the contrary, the numerical parameters set forth inthe specification and attached claims are approximations that may varydepending upon the desired properties sought to be obtained by thepresent invention. At the very least, and not as an attempt to limit theapplication of the doctrine of equivalents to the scope of the claims,each numerical parameter should be construed in light of the number ofsignificant digits and ordinary rounding approaches. For example, termssuch as about, approximately, substantially, and the like may representa percentage relative deviation, in various embodiments, of ±1%, ±5%,±10%, or ±20%.

The above description discloses several methods and materials of thepresent disclosure. The present disclosure is susceptible tomodifications in the methods and materials, as well as alterations inthe fabrication methods and equipment. Such modifications will becomeapparent to those skilled in the art from a consideration of thisdisclosure. Consequently, it is not intended that the present disclosurebe limited to the specific embodiments disclosed herein, but that itcovers all modifications and alternatives coming within the true scopeand spirit of the present disclosure.

What is claimed is:
 1. An injector for a rocket combustion chamber, theinjector comprising: a housing defining a longitudinal axis and having aproximal end and a distal end, the housing comprising a variable innerwidth; a poppet residing in the housing, the poppet capable of movingalong the longitudinal axis, the poppet comprising a variable outerwidth forming a variable annular flow path between the variable outerwidth of the poppet and the variable inner width of the housing, thevariable annular flow path configured for a propellant to flowtherethrough; and a spring configured to bias the poppet causing a firstforce on the poppet, wherein flow of the propellant along the variableannular flow path causes a second force on the poppet, and wherein thefirst force and the second force move the poppet inside the housingalong the longitudinal axis causing an area of the variable annular flowpath to change.
 2. The injector of claim 1, wherein the propellantenters the housing through a plurality of ports distributed annularlyabout a sidewall of the housing.
 3. The injector of claim 1 furthercomprising a bellows positioned at a proximal end of the housing outsideof a propellant flow path, with a distal end of the bellows facing aproximal end of the poppet.
 4. The injector of claim 3, wherein thebellows comprises a plurality of openings configured to allow thepropellant to flow into and out of an interior of the bellows.
 5. Theinjector of claim 1, wherein the spring is disposed about a proximal endof the poppet within the housing, and wherein the variable annular flowpath is located at a distal end of the poppet.
 6. The injector of claim1, wherein the first force and the second force are in directionsparallel with the longitudinal axis.
 7. The injector of claim 1 furthercomprising a first stop and a second stop configured to limit axialtravel of the poppet within the housing, to thereby limit a maximum areaand a minimum area of the variable annular flow path.
 8. An injector fora rocket combustion chamber, the injector comprising: a flow pathconfigured for a propellant to flow through, the flow path boundedoutwardly by a variable width section protruding inwardly within ahousing, the flow path bounded inwardly by a poppet within the housingand having a variable poppet width section protruding outwardly, thevariable width section and the variable poppet width section defining anannular flow path section around the variable poppet width section,wherein a spring causes a first force on the poppet, wherein flow of thepropellant through the annular flow path section causes a second forceon the poppet, and wherein axial movement of the poppet inside thehousing due to the first force and the second force changes across-sectional area of the annular flow path section.
 9. The injectorof claim 8 further comprising entrance ports distributed about asidewall of the housing near the variable width section and configuredto receive the propellant therethrough.
 10. The injector of claim 8,wherein the cross-sectional area of the annular flow path section iscircular.
 11. The injector of claim 8, wherein the cross-sectional areaof the annular flow path section defines a donut shape.
 12. The injectorof claim 8 further comprising a bellows configured to dampen movement ofthe poppet and comprising a series of openings configured to receivepropellant.
 13. The injector of claim 8, wherein the variable widthsection within the housing reduces in width in an axial direction to aminimum width throat portion and increases in width from the minimumwidth throat portion in the axial direction.
 14. The injector of claim8, wherein the variable poppet width section increases in width in anaxial direction to a minimum width portion and increases in width fromthe minimum width portion in the axial direction.
 15. The injector ofclaim 8 further comprising a guide within the housing configured toradially support the poppet during axial movement of the poppet throughthe guide.
 16. A method of passively varying a flow rate of propellantinjected into a rocket combustion chamber, the method comprising:receiving the propellant into a housing of an injector; applying abiasing force with a spring to a poppet within the housing; causing thepropellant to flow at a first flow rate around the poppet in a firstposition within the housing, the poppet in the first position defining afirst flow area; and causing the propellant to flow at a second flowrate around the poppet to thereby cause the poppet to move from thefirst position to a second position within the housing, the poppet inthe second position defining a second flow area, and wherein the secondflow area is different from the first flow area.
 17. The method of claim16 further comprising dampening movement of the poppet with a bellows.18. The method of claim 16 further comprising varying the biasing forcefrom the spring on the poppet as the poppet moves from the firstposition to the second position.
 19. The method of claim 16, wherein thesecond flow rate is greater than the first flow rate, and wherein thesecond flow area is greater than the first flow area.
 20. The method ofclaim 16 further comprising maintaining a ratio of A) a pressure dropacross the injector to B) a pressure within the combustion chamber influid communication with the injector within a target range of 15% to25% across a range of flow rates of the propellant.